Abstract
Ducts containing a tube bundle undergo acoustic resonant vibrations. It is more reasonable to think that the vibration is a kind of mutual excited vibration between fluid dynamic force and sound pressre(1). In this case, it is very important to obtain the damping ratio and the natural frequency of sound pressure in the duct. Frequency responses of the sound pressure were calculated by boundary element method. Natural frequency and damping ratio were obtained by the least error method using the frequency response curve. Calculated natural frequencies in closed square box with no tube bundle are in good agreement with theoretical values and the damping ratios are very small. Square box with tube bundle also has very small damping ratio but the natural frequency increases with the tube diameter. In the case of box having holes, the natural frequency and damping ratio increases with the open rate of the holes. Natural frequencies and damping ratios of the other type of boxes and tube bundles were also calculated and the results are shown in this paper.
